Protheses with selectively welded crossing strands

Abstract

A body implantable stent is formed of a plurality of strands arranged in two sets of coaxial helices, wound in opposite directions to form multiple crossings. At selected crossings, the adjacent strands are welded to one another, while at the remaining crossings the strands are free for limited movement relative to one another. The welds are formed in patterns that preferably enhance radial strength and rigidity, while having a minimal impact on axial bending flexibility. Preferred weld patterns in this regard include rings or circumferential rows, and helices, particularly with a steeper pitch than that of the strands. Stent fabrication preferably involves resistance welding at the crossings, and use of a tool to reuniformly compress the stent around and against the distal end region of a balloon catheter used later to deliver the stent to a treatment site.

What is claimed is: 
     
       1. A body insertable prosthesis, including: a plurality of substantially helical strands forming a generally tubular structure, with the strands further forming multiple crossings of adjacent ones of the strands, including a plurality of secured crossings at which the adjacent strands are joined and plurality of unsecured crossings at which the adjacent strands are free for limited travel relative to one another;   wherein the secured crossings, at least throughout a selected axial region of the tubular structure, are arranged in a pattern to selectively alter a radial stiffness of the tubular structure along the selected region; and   wherein the tubular structure is radially enlargeable from a reduced-radius delivery state to a radially-enlarged state to achieve contact with tissue at a treatment site within a body lumen.   
     
     
       2. The prosthesis of claim 1 wherein: said pattern is selected to increase radial stiffness with substantially less influence on an axial bending stiffness of the tubular structure.   
     
     
       3. The prosthesis of claim 1 wherein: the pattern is helical.   
     
     
       4. The prosthesis of claim 1 wherein: the pattern is comprised of a plurality of circumferential rows of the secured crossings.   
     
     
       5. The prosthesis of claim 1 wherein: the secured crossings are formed at a density, in terms of a ratio of secured crossings to all crossings, in the range of about 10-90 percent.   
     
     
       6. The prosthesis of claim 5 wherein: said density is about 40-80 percent.   
     
     
       7. The prosthesis of claim 1 wherein: the secured crossings are characterized by welds of the adjacent strands.   
     
     
       8. The prosthesis of claim 1 wherein: the stands form a latticework of first and second sets of helices running in opposite directions.   
     
     
       9. The prosthesis of claim 8 wherein: the helical strands are interbraided.   
     
     
       10. The prosthesis of claim 8 wherein: the helices have substantially the same strand pitch relative to a longitudinal axis of the latticework.   
     
     
       11. The prosthesis of claim 10 wherein: the pattern is helical.   
     
     
       12. The prosthesis of claim 11 wherein: the helical pattern has an effective pitch, relative to the longitudinal axis, greater than the strand pitch.   
     
     
       13. The prosthesis of claim 11 wherein: the effective pitch is at least about 45 degrees, and the strand pitch is in the range of about 15-37.5 degrees.   
     
     
       14. The prosthesis of claim 1 wherein: said pattern is selected to controllably determine the radial stiffness.   
     
     
       15. The prosthesis of claim 1 wherein: the selected axial region encompasses substantially the entire tubular structure.   
     
     
       16. The prosthesis of claim 1 wherein: the selected axial region comprises a medial region of the tubular structure.   
     
     
       17. The prosthesis of claim 16 wherein: the tubular structure consists substantially of the medial region and first and second end regions on opposite sides of the medial region, said secured crossings are formed at a first density in the medial region and at a second density in the end regions, and wherein the first density is less than the second density.   
     
     
       18. The prosthesis of claim 17 wherein: said second density is approximately one hundred percent.   
     
     
       19. The prosthesis of claim 1 wherein: the strands are formed of a flexible material.   
     
     
       20. The prosthesis of claim 1 wherein: said strands are formed of a plastically deformable material.   
     
     
       21. The prosthesis of claim 1 wherein: said strands are formed of at least one of the materials from a group comprising: tantalum, gold, silver, titanium, steel, a cobalt-based alloy, and a titanium nickel alloy.   
     
     
       22. A medical device including the prosthesis of claim 1, and further including: an elongate inflatable balloon, in a substantially aspirated condition, surrounded by the tubular structure in the reduced-radius delivery state; and   a means for providing an inflation fluid to the balloon under pressure, to expand the balloon and thereby expand the tubular structure to the radially-enlarged state.   
     
     
       23. The device of claim 22 further including: an elongate and flexible catheter supporting the elongate balloon along a distal end region of the catheter; wherein the means for providing fluid includes a fluid source near a proximal end of the catheter, and a balloon inflation lumen fluid coupled to the fluid source and to the balloon.